1.CDLOD
2.Geometry Clipmap
3.Geometry CDClipmap(Crest Ocean在Clipmap基础上改进的)
参考: https://github.com/fstrugar/CDLOD
https://github.com/fstrugar/CDLOD/blob/master/cdlod_paper_latest.pdf
参考: http://mikejsavage.co.uk/blog/geometry-clipmaps.html
https://hhoppe.com/proj/geomclipmap/